There are a few reasons why you might need to import Gmail to Gmail.
To consolidate your emails. If you have multiple Gmail accounts, you can import them into one account to make it easier to manage your emails.
To back up your emails. Importing your Gmail emails to another account can be a good way to back them up in case something happens to your primary account.
To transfer emails to a new computer. If you are switching to a new computer, you can import your Gmail emails to the new computer so that you do not lose them.
To change email providers. If you are changing email providers, you can import your Gmail emails to the new provider so that you do not have to start from scratch.
Greetings,
Peter